The question is repeatedly asked: What's the "sweet spot" to book air travel to get the best fares, availability, most desirable seats, etc...
The short answer is: It depends!
Not being big on answering question with questions, we will lay it out:
Factors that are considered to answer:
1) What is the origin and destination?
2) What is the season (high/low or shoulder?
3) Is it a high demand resort or business destination?
4) International or domestic?
5) Is it a competitive route?
6) Direct or Connections flight(s)?
The common misconception with travelers is that the earlier you book, the cheaper the fare...not true. For example, booking 10 months in advance may not get you the lowest fare as airlines believe that they have a lot of time to sell the seat.
For international travel 3 weeks-3 months would normally yield a lower fare.
Domestic tickets are more subjective to a variety of airline algorithms that vary due to all above factors...